Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1155 PM EDT Wednesday Oct 26 2016
Low pressure will track along the mi/OH border early this morning.
Widespread IFR ceilings extend along and north of this sfc low with
the influx of moisture along and north of the low track. Recent
model soundings along with area observations suggest IFR ceilings
will prevail through mid to late morning. Mid level dry air will
continue to overspread se mi during the early morning. This will
cause the residual light rain showers to diminish to drizzle. Cold
air advection in the wake of the departing sfc low later in the
morning will allow a slight upward trend in ceiling heights during
the day thurs.
For dtw...observations indicate the IFR ceilings will move back into
Metro by taf issuance. The easterly winds will slowly weaken heading
toward daybreak as the sfc gradient relaxes with the approach of the
//Dtw threshold probabilities...
* high in ceilings below 5000 feet today.
issued at Detroit/Pontiac Michigan 752 PM EDT Wed Oct 26 2016
Portions of the forecast area got an early taste of winter today.
To recap, the northern Detroit suburbs and points north saw a mix
of snow and rain through a good portion of the afternoon. The Tri
Cities and the central thumb had almost entirely all snow. The
snow was actually falling at a moderate pace at times. The warm
ground temps inhibited accumulations on roads. However, there
have been reports of one to almost two inches on elevated surfaces
extending along a line from roughly Midland County to Lapeer
County. This does not break the earliest record of measurable snow
in Southeast Michigan which occurred on October 12, 2006.
A strong influx of deep layer moisture into lower mi has been
occuring in advance of a compact mid level wave now over Wisconsin.
This moisture has been intersecting a mid level frontal boundary
over lower mi. Meanwhile, easterly surface flow throughout the
afternoon (coming from srn Ontario where sfc dewpoints are in the
20s) sustained enough low level dry air to bring wet bulb zero
heights below 1k ft within the region of strongest ascent (from
central mi into the thumb). This forcing held nearly stationary
for much of the afternoon, leading to a localized region of
significant cooling and persistent snowfall.
The influx of deep moisture transport will persist through roughly
06z before it slowly shifts east. There has already been some
disruption to the mid level fgen across the north. Although
recent hi res solutions suggest the fgen holding together and
possibly reintensifying during the night, strengthening low level
moisture advection will boost wet bulb zero heights during the
course of the night. There has been a subtle upward trend in sfc
dewpoints across the the forecast area which supports this. Recent
model soundings suggest this moistening will lift wet bulb zero
heights above 1200 ft and thus transition lingering snow over to all
rain by midnight. The mid level dry slot already punching into lake
mi will then rotate across most of the area late tonight, transition
rain showers over to drizzle. Overall the current forecast has a
reasonable handle on this. Just some minor updates to temps and
timing of the change over to rain in the north will be made.
issued at 342 PM EDT Wed Oct 26 2016
An upper level shortwave trough is now tracking into the northern
Great Lakes with the associated surface low over western Illinois as
of 19z. The leading flank of precipitation has developed with good
moisture advection over the warm front with an active 850-700mb fgen
band and supporting region of isentropic ascent. Overall the lead
band of showers is behaving as expected, outside of a bit more sleet
at the onset as dewpoints in the upper 20s kept wet bulb temps well
below the 40 degree temps around the region. As the deeper moisture
moves in and dewpoints rise to the mid 30s, precip will change to
all rain for the duration of the event this evening and tonight for
most locations. The Thumb and Saginaw may hold onto the mix precip
longer as they are farther removed from the low itself which will
track along the Michigan/Ohio border. Soundings also support saturation in
the ice Crystal layer for several more hours before temperatures
warm slightly and moisture no longer resides in the layer below -
10c. Early reports out of the Cadillac area are of some minor slushy
accumulation from the heavier bands. Cannot completely rule out some
minor slush on the ground around Midland through this evening, but
won't last long before melting. Mixed precip should end later this
evening turning to all rain for the overnight period as higher
dewpoints work into the area closer to the center of the low. A dry
slot lifting into southwest lower looks like it has reached it's
peak northward extent as showers regenerated filling it back in.
This will result in a brief lull for locations south of i94 this
afternoon but additional showers will slide through tonight.
The heaviest showers will work off to the east early Thursday
morning with some scattered showers lingering on through the
morning. Cold air advection with cyclonic flow behind the system
will drop 850mb temps from about 1c this afternoon to -4c on
Thursday which will result in strong low level lapse rates. Moisture
will locked below 800mb in this active region which will result in
some afternoon showers. Models are advertising some cape in the
afternoon which may result in some graupel forming in the stronger
showers. Will not see much of an improvement in temperatures
Thursday with highs only in the mid/upper 40s. Zonal flow in the mid
level will bring a Flat Ridge and warmer air into the area Friday
resulting in highs back in the mid 50s. The next wave will dive from
the northern plains through the northern Great Lakes Friday night.
Looks dry on the south side of the system over lower Michigan but a cold
front sweeping across the area late Friday night into Saturday
morning will need a chance pop.
Low pressure centered over Upper Michigan on Friday afternoon will
continue to track to the east east through the weekend. Weak chances
for precipitation are possible during the day on Saturday,
especially over the northern thumb areas. High pressure returns for
Sunday/Monday. At this time, models are showing a stronger weather
system that will begin moving into Southeast Michigan on the late
Low pressure will track from northern Illinois to extreme southern
Ontario by Thursday morning. Easterly winds will continue to
strengthen this evening and overnight as the low approaches. Speeds
will decrease after about 5 am over Lake St Clair and Western Lake
Erie as the low passes overhead, while remaining strong and turning
more to the northeast over Lake Huron. Gusts this evening through
Thursday look to remain under gale force with peak winds around 30
knots. The strong and persistent onshore flow will also generate
large waves over the nearshore waters, which will continue into
Thursday for Lake Huron. High pressure will slowly build into the
central Great Lakes late Thursday and Thursday night, allowing winds
and waves to decrease.
Numerous rain showers, at times mixed with sleet or snow, will
continue to spread into Southeast Michigan through the remainder of
the afternoon. Coverage and intensity will increase this evening and
overnight with widespread and steadier rainfall expected. Potential
for snow/sleet will also decrease this evening from south to north
as deeper moisture and higher dewpoints arrive. Rain will taper off
to showers tomorrow morning before ending tomorrow afternoon.
Rainfall totals are still expected to range between one-half and
three-quarters of an inch. Dry weather is expected Thursday night
and Friday, with just a small chance of light showers Friday night.
Lake Huron...Small Craft Advisory until 10 PM EDT Thursday for lhz421-422-
Lake St Clair...Small Craft Advisory until 4 am EDT Thursday for lcz460.
Michigan waters of Lake Erie...Small Craft Advisory until 4 am EDT Thursday for lez444.
You can obtain your latest National Weather Service forecasts online